1. Technical Field
The present invention relates to a resonator element that excites a thickness shear vibration, a resonator, an electronic device, an electronic apparatus, a mobile body and a method of manufacturing a resonator element.
2. Related Art
Since quartz crystal resonators using a quartz crystal resonator element in which a main vibration is excited by a thickness shear vibration are suitable for a decrease in size and a rise in frequency, and have excellent frequency-temperature characteristics, the quartz crystal resonators are used in many fields of oscillators, electronic apparatus and the like. Particularly, in recent years, with decreases in size and thickness of various electronic apparatus such as a cellular phone and a computer, there has also been a great need for further decreases in size and thickness of the quartz crystal resonators used in these electronic apparatus.
JP-A-2011-19206 discloses a method of manufacturing a plurality of quartz crystal resonator elements in a batch processing mode from a large-size quartz crystal substrate, using a photolithography technique and an etching technique at the time of the formation of a contour shape and an excitation electrode of the quartz crystal resonator element.
However, when a decrease in size of the quartz crystal resonator is attempted to achieve, there has been a problem in that vibration energy leaks due to the close distance between a vibration region and a holding portion to thereby reduce CI (quartz crystal impedance=equivalent resistance of quartz crystal resonator), an unnecessary spurious vibration such as a thickness bending vibration dependent on the profile dimensions of a vibration portion is generated in the vicinity of a resonance frequency of a thickness shear vibration which is a main vibration, and a discontinuous fluctuation in frequency and CI for a temperature change, that is, a so-called anomalous activity dip or the like occurs. Consequently, JP-A-2010-62723 proposes a method of avoid a reduction in CI or an anomalous activity dip with a decrease in size by forming a quartz crystal resonator element having a mesa structure, and discloses a method of manufacturing a plurality of quartz crystal resonator elements in a batch processing mode from a large-size quartz crystal substrate, using a photolithography technique and an etching technique at the time of the formation of a contour shape and an excitation electrode of the quartz crystal resonator element, in order to achieve mass production or a reduction in cost.
When the quartz crystal resonator element is manufactured by the manufacturing method disclosed in JP-A-2011-19206 or JP-A-2010-62723, the contour shape is uniform and the excitation electrode is disposed at a predetermined position with a high degree of accuracy, thereby allowing a quartz crystal resonator element that sufficiently satisfies a specification standard such as CI and temperature characteristics to be obtained. However, there has been a problem in that the Drive Level Dependence (DLD) characteristics of the quartz crystal resonator element influencing the start-up of an oscillator in which the quartz crystal resonator element is mounted are deteriorated considerably, and the manufacturing yield rate is lowered remarkably.